The invention relates to a device for use with fluid-filled machines required to run in arduous conditions, such as a fluid-filled motor driving a downhole pump in an oil-well, for example.
In such a machine, the following requirements are required to be met:
(i) the fluid pressure inside the machine to be kept above ambient pressure irrespective of any change in pressure or temperature before and during installation;
(ii) the internal and ambient pressures to be equalized when the shaft of the machine is initially run up to speed after installation;
and
(iii) no deleterious particles to contaminate the internal fluid.